1. Field of the Invention
The present disclosure relates to a vibration motor.
2. Description of the Related Art
From the past, a brushless vibration motor of a thin coin type has been used for a silent notification device of mobile communication devices and the like, or for other purposes. In this vibration motor, a spacer is provided around a shaft on a base part to which the shaft is fixed, as disclosed in Japanese Patent Application Publication No. 2008-289268 and Japanese Patent Application Publication No. 2006-94643, etc. A lower end portion of a rotating part, which is rotatably attached to the shaft, is in contact with the spacer. A coil part is also provided around the spacer.
For example, in Japanese Patent Application Publication No. 2008-289268, an eccentric rotor R is rotatably mounted on an axis 2 through a thrust washer SW and a bearing 9. The axis 2 is fixed to a bracket 1, and the thrust washer SW is attached to the axis 2 on the bracket 1. Four air-core armature coils 5 are securely mounted on the bracket 1 at a radially outer side of the axis 2 and the thrust washer SW.
In Japanese Patent Application Publication No. 2006-94643, a sleeve metal 14, which is press-fitted to a center portion of a rotor yoke 13, is fitted to a shaft 6. A washer 16 is fitted to the shaft 6 at a portion between a base member 3 and the sleeve metal 14. With this, the rotor yoke 13 can be rotatably supported on the base member 3. Further, two coils 8, which are facing each other across the shaft 6 and the washer 16, are mounted on a circuit board 7 which is fixed onto the base member 3.
In recent years, a further minimization for a coin type vibration motor has been required in accordance with the minimization of mobile communication devices, etc. However, if the diameter of the motor is simply reduced, the volume of the coil part should be reduced, and thereby motor torque will be reduced and consequently the amount of vibration will also be reduced. Otherwise, the amount of vibration will be reduced by the decreased volume of an eccentric weight.